Field Recording – Thunderstorms

 

Most field recordists (and photographers)  have a natural affinity for recording thunderstorms; possibly due to the tremendous challenge presented by them. Thunderstorms are unpredictable beasts, especially when in the vicinity of the recorder. So let’s go through some of the difficulties in getting good audio recordings of these storms.

Often, but not always, we have the rain, and as you may or may not know, microphones and audio recorders are sensitive electronic devices and they do not like mixing with water or even damp atmospheres. The first indication that the microphone is becoming sick is by the tell-tale ‘plopping’ sounds heard whilst recording. The next problem should never be underestimated and is usually a natural instinct of the field recordist, and that is not to stand outside in a thunderstorm whilst holding onto a metal-cased microphone surrounded by wire cables, audio recorder and wearing headphones -  it’s too late when your hair stands on end and you hear a clicking sound in your headphones! As we all know thunderstorms can produce some really great and intense cracking sounds, followed by some powerful low-frequency rumbles. All of  these add up to high sound pressure levels (SPL) and without good quality microphones which are capable of handling these SPLs, then distortion will be evident in the captured audio recording. Some microphones have pad circuits which allow the recordist to switch in an attenuation circuit, thereby reducing the level of sound recorded, in an attempt to reduce distortion. Unfortunately this does not help produce a good quality recording, as it merely reduces the level of all sounds even the quiet ones, resulting in a loss of the surrounding low ambient sound levels. Another way of preventing distortion of the recorded sound is by switching in a limiter or compression circuit on the audio recorder, which in layman’s terms just squashes any sound louder than a predetermined threshold level back down to that threshold, thereby avoiding distortion. However this method restricts the dynamic range (quietest to loudest sound level) recorded, producing a weak sound recording, lacking that ear-shattering sharp crack heard from a close thunder-clap.  Bearing in mind the problem of rain and the vulnerability of the recordist standing outside in a thunderstorm, it often makes sense to record from a place of shelter from both rain and lightning (don’t even think of standing under trees – far too dangerous).  A place of shelter however, also comes with its own problem, that of noise and sound colouration. If you’ve ever stood under a plastic or sheet covered shelter in heavy rain, then you will know what I mean; the sound of the rain can often drown out all other sounds and the type of roof or sheet covering will produce its own sound colour which imparts an unatural sound to the recorded storm. The final problem with recording thunderstorms, is that of unpredictability. What this means is, that you’ve just got your levels set just right on the audio recorder and everything is going well, with the storm heading your way nicely; until there is an almighty crack nearby which peaks out or clips the recording. One of the best strikes you’ve heard all year, only to be ruined by the clipped (distorted) signal. That really does annoy a field recordist! Never mind next time lucky.

Here are two parts of the same thunderstorm recorded over Diss, Norfolk, UK. at 03:23 hrs 28 May 2008. Recording made with Rode NT1A & NT2A (figure 8 pattern) microphones mounted in tandem on tripod and fed via RME Quadmic preamp to Edirol R-4 recorder. Original audio recorded in 24 bit 44Khz 2 channel mono mixed down to mid-side stereo.

Audio 01: Starts with a neighbourhood dog barking. Recording in this part was made outside despite some initial rain. (Unfortunately some artifacts are present in this low resolution mp3 file)

Audio 02: In this part the rain was too heavy for the equipment to remain outside, so was moved into the conservatory with plastic-sheet roof and the french-doors open. Listen to the different sound colouration between the two parts. There is a nearby lightning strike just past the 5 min mark.

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